File:A text-book of human physiology (1906) (14747366476).jpg

Identifier: textbookofhumanp00tige (find matches)
Title: A text-book of human physiology
Year: 1906 (1900s)
Authors: Tigerstedt, Robert, 1853-1923 Murlin, John R. (John Raymond), b. 1874, tr
Subjects: Physiology
Publisher: New York and London, D. Appleton and Co.
Contributing Library: Columbia University Libraries
Digitizing Sponsor: Open Knowledge Commons

View Book Page: Book Viewer
About This Book: Catalog Entry
View All Images: All Images From Book
Click here to view book online to see this illustration in context in a browseable online version of this book.

Text Appearing Before Image:
n the heart is accelerated by division of both vagi, or by stimulationof the accelerator nerves, it may or may not expel more blood in a given THE FLOW OF BLOOD IN THE ARTERIES 205 time. If it does, the blood pressure increases (supposing that the caliber ofthe vessels has not changed) ; if not, the pressure remains the same. Fora quicker rate does not necessarily imply greater energy of the heart beat,and so does not of necessity produce a greater output. Now it is evident thatunless the total output in a unit time is increased, the quantity of bloodcoming back to the heart between two systoles is less with a rapid pulse thanwith a slow one, or, in other words, the pulse volume is less. Hence, theblood pressure following acceleration will depend upon the reciprocal relationbetween the increase of pulse rate and the decrease of pulse volume. Direct investigations of this subject have resulted in showing that nogeneral law can be formulated. If a large quantity of blood is found in the
Text Appearing After Image:
Fig. 77.—Blood pressure curve, showing a slight fall under feeble stimulation of the vagus.To be read from right to left. The time of stimulation is indicated by the two verticallines. I 1 = ten seconds. great veins, and is only waiting an opportunity to get into the heart, and ifthe resistance in the arterial system is sufficiently high, acceleration mayproduce a considerable increase in blood pressure. If these conditions arenot fulfilled, the increased frequency will occasion no rise in pressure worthmentioning. 2. Resistance in the Arteries.—It is evident that with a given heart energy,if the resistance in the vessels decreases, the pressure also must decrease. Ifthe resistance increases the pressure also must increase. A fall in pressure in consequence of diminished resistance occurs, if thevessels in a large vascular region lose their tonus. Not only the arteries, butthe veins as well are to be considered as taking a part in this; for the lat-ter possess a certain tonus with

Note About Images